A large-scale analysis of three major prospective cohort studies involving middle-aged U.S. adults found that increased intake of olive oil was inversely associated with long-term body weight changes. Conversely, increased consumption of other added fats, butter, margarine, and refined grains showed positive associations with weight gain. These findings support current dietary guidelines emphasizing fat quality over quantity, and suggest that substituting olive oil for other fats may be a beneficial strategy for weight management among middle-aged U.S. adults.